1. Field of the Invention
The invention relates to an exposure device which has a microscope for determining mask alignment marks and a microscope for determining workpiece alignment marks and in which, using the two microscopes, positioning of the mask alignment marks and the workpiece alignment marks relative to one another is carried out. The invention relates especially to an exposure device in which the workpiece is divided into several exposure zones and which is used as an exposure device for incremental exposure of each exposure zone in a suitable manner.
2. Description of the Prior Art
In the production of a device for producing a semiconductor, a process is carried out in which a mask pattern which has been formed on a mask is exposed onto a wafer (hereinafter called a xe2x80x9cworkpiecexe2x80x9d) as the substrate which is to be treated. In this process, the following is steps are performed:
the area to be exposed on the wafer is divided into several areas;
the mask pattern is projected onto the above described areas which have been produced by division;
a workpiece carrier on which the wafer has been seated is moved by a given amount; and
the above described exposure areas which have been formed by division are moved in rows to the exposure position and incrementally exposed.
This process is generally called incremental exposure or xe2x80x9cstep and repeatxe2x80x9d exposure. An exposure device which carries out this exposure is called an xe2x80x9cincremental exposure devicexe2x80x9d or xe2x80x9cstepperxe2x80x9d (hereinafter called an xe2x80x9cincremental exposure devicexe2x80x9d).
The arrangement and operation of the above described incremental exposure device is described below using FIG. 6. In this figure, the frame and the like which support the respective material components are not shown. In the figure, a light irradiation part 10, from which exposure light emerges, has an optical system, such as a lamp 10a, a focusing mirror 10b and the like.
The exposure light emerging from the light irradiation part 10 is emitted onto a mask M on a mask carrier 11. The mask pattern which has been formed on the mask M is imaged via a projection lens 12 onto a workpiece W on a workpiece carrier 13 and exposed. On the workpiece carrier 13, there is a device 13a for movement in the X-Y directions (XY are two orthogonally intersecting axes on a plane which is perpendicular to the page of the drawing). By incrementally moving the workpiece carrier 13, the workpiece W is moved from one area to the other area, which areas are formed by division, and thus, the workpiece W is exposed. If necessary, there can be a device for moving the workpiece carrier 13 in the xcex8-Z direction (xcex8: rotation around an axis perpendicular to the X-Y plane, Z: direction of the optical axis of the exposure light). Regulation of the imaging position of the mask pattern is carried out by movement either of the mask M, the projection lens 12 or the workpiece carrier 13 in the direction of the optical axis (Z-direction).
Before exposure of the workpiece W, positioning of the mask M relative to the workpiece W is carried out in order to expose the mask pattern at a given position of the workpiece W. This positioning is carried out by determining the positions of mask alignment marks MAM formed in the mask (hereinafter called mask marks) and the workpiece alignment marks WAM formed in the workpiece W (hereinafter called workpiece marks) and by moving the mask M and/or the workpiece W such that the two marks attain a given positional relationship (for example, are aligned with one another).
Therefore, there are two microscopes 14 for determining the mask marks (hereinafter called xe2x80x9cmicroscopes for mask marksxe2x80x9d) which determine the mask marks MAM, and one microscope 15 for determining the workpiece marks (hereinafter called the xe2x80x9cmicroscope for workpiece marksxe2x80x9d) which determines the workpiece marks WAM.
The microscopes for mask marks 14 are positioned to be removable or insertable between the light irradiation part 10 and the mask M. The position relationship of the two microscopes for mask marks 14 is set beforehand and the coordinate systems of the two microscopes agree with one another. Normally, there are two microscopes for mask marks 14. The reason for this is to determine two mask marks MAM at the same time, to measure the deviation of the mask M in the xcex8 direction and to correct the amount of deviation. If there is a device for extensive movement of the microscope for mask marks 14 in the X-Y directions, only one microscope for mask marks 14 is sufficient. However, the mask carrier 11 is normally not made such that it can move to a large extent. If it is made such that it can move to a large extent, the precision of the movement is problematical and the arrangement of the devices complicated. Therefore, normally two microscopes for mask marks 14 are used.
In the microscope for mask marks 14, there is an alignment light source 14a which emits alignment light. The alignment light is reflected via the mask M and the projection lens 12 by workpiece W or by the workpiece carrier 13 when the mask M is present, and via the mask M if again the mask M and projection lens 12 are present, enters the CCD camera 14b of the microscope for mask marks 14.
The microscope for workpiece marks 15 is located integrally with a projection lens 12. In the microscope for workpiece marks 15, there is also an alignment light source 15a which emits alignment light. The alignment light is reflected by the workpiece W or the workpiece carrier 13 and enters the CCD camera 15b of the microscope for workpiece marks 15. Here, it is assumed that, with respect to the X-Y directions of motion of the workpiece carrier 13, there is square parallelism of the X-Y coordinates of the two microscopes 14 for the mask marks and of the microscope 14 for the workpiece marks 15. The pictures which have been received by the CCD cameras 14b, 15b, which are located in the microscopes 14, 15, are sent to a controller 16. The controller 16 acquires the position information of the respective mark by image processing of the determined mask marks MAM or the workpiece marks WAM.
The sequence of positioning of the mask relative to the workpiece in the above described exposure device is described below.
(1) Base Line Correction
In the exposure device shown in FIG. 6, the microscope for determining the mask marks and the microscope for determining the workpiece marks differ from one another. Therefore, the mask and the workpiece cannot be positioned relative to one another if the position relationship of the two with respect to each other is not known exactly.
Furthermore, since the positional relationship of the two with respect to one another is changed by thermal expansion which is caused by the ambient conditions and the like of the device, generally confirmation and correction must be carried out. This activity of correction of the relative positions of the microscope for mask marks 14 and of the microscope for the workpiece marks 15 relative to one another is called xe2x80x9cbaseline correctionxe2x80x9d here.
(i) As shown in FIG. 7(a), in the workpiece carrier 13 a reference mark BM (only one mark is sufficient) is formed.
(ii) The workpiece carrier 13 is moved to a preset position such that the above described reference mark BM extends into the field of vision of one of the microscopes 14 for the mask marks. The microscope for mask marks 14 emits alignment light. The reference mark BM is illuminated via the projection lens 12. The light reflected by the reference mark BM is received via the projection lens 12 by the CCD camera 14b of the microscope 14 for mask marks. FIG. 7(a) shows the reference marks BM received by the CCD camera 14b. 
(iii) The reference mark image received by the CCD camera 14b is sent to the controller 16 and is subjected to image processing. Thus, the position of the microscope 14 for the mask marks is computed at the coordinates and stored in the controller 16. The position coordinates of the reference mark BM with respect to the middle of the visual field of the microscope 14 for mask marks are designated (x0, y0). The line which forms between the centers of the visual fields of the two microscopes for mask marks is located parallel to the direction of the X-axis or the Y-axis of the workpiece carrier 13. It need not be asked which of the microscopes is used for the mask marks.
(iv) Then, as shown in FIG. 7(b), the workpiece carrier 13 is moved such that the reference mark BM extends into the visual field of the microscope 15 for the workpiece marks. The amount (xcex94X0, xcex94Y0) of this motion of the workpiece carrier 13 is determined beforehand as computed data based on the position of the visual field of the microscope 14 for mask marks and based on the position of the visual field of the microscope 15 for the workpiece marks.
(v) The reference mark BM is determined with the microscope 15 for the workpiece marks. The microscope 15 for the workpiece marks emits alignment light, by which the reference mark BM is illuminated. The light reflected by the reference mark BM is received by the CCD camera 15b of the microscope 15 for the workpiece marks. In FIG. 7(b) the reference mark BM received by the CCD camera 15b is shown. The determined reference mark BM is sent in the above described manner to the controller 16 and is subjected to image processing. The position of the reference mark BM at the coordinates of the microscope 15 for the workpiece marks is computed and stored in the controller 16. The position coordinates of the reference mark BM with respect to the center of the visual field for the microscope 15 for workpiece marks are designated here by (x1, y1).
(vi) The difference xcex94x=x0xe2x88x92x1, xcex94y=y0xe2x88x92y1 between the position (x0, y0) of the reference mark in the visual field of the microscope for mask marks 14 and the position (x1, y1) of the reference mark in the visual field of the microscope for workpiece marks represents the amount of deviation between the microscope for mask marks 14 and the microscope for workpiece marks 15. This amount of deviation represents the amount of baseline correction. If, for example, xcex94x=0, xcex94y=0, the amount of baseline correction is 0. The microscope 14 for the mask marks and the microscope 15 for workpiece marks are moved apart here according to the above described computed data (the value which corresponds to the amount of motion (xcex94X0, xcex94Y0) of the workpiece carrier 13).
(2) Positioning of the Mask to the Workpiece
As was described above, positioning of the mask M relative to the workpiece W is performed in the manner described below after the amount of baseline correction has been determined.
(i) As is shown in FIG. 8(a), the mask M is installed in the mask carrier 11. Furthermore, the workpiece W on which the workpiece marks WAM are formed is placed on the workpiece carrier 13.
(ii) Two microscopes for mask marks 14 are inserted (in FIGS. 8(a) and 8(b), only one microscope 14 for mask marks is shown). The mask marks MAM are determined by the two microscopes for mask marks, the mask carrier 11 is moved, correction in the xcex8 direction is performed and two mask marks MAM are made parallel to the X axis (can also be the Y axis).
(iii) As is shown in FIG. 8(b), the workpiece carrier 13 is moved by the microscope 15 for workpiece marks to the position at which the workpiece marks WAM on the workpiece W can be determined. Alignment light is emitted onto the workpiece mark WAM by the microscope for workpiece marks 15. As was described above, the position coordinates (x3, y3) of the workpiece mark WAM are determined, the center of the visual field in the visual field of the microscope 15 for workpiece marks being regarded as the zero point. FIG. 8(b) shows the workpiece mark WAM received by the CCD camera 15b. 
(iv) Then, as shown in FIG. 8(a), alignment light is emitted from the microscope 14 for the mask marks. The images of the mask marks MAM are received by the CCD camera 14b of the microscope 14 for mask marks.
(v) The mask marks MAM are subjected to image processing. The position coordinates (x2, y2) of the mask marks are computed, the center of the visual field in the visual field of the microscope 14 for mask marks being regarded as the zero point.
(vi) The amount of deviation (xcex94X0+xcex94x, xcex94Y0+xcex94y) of the microscope 15 for workpiece marks from the microscope 14 for mask marks is determined by the above described baseline correction. This deviation is called (xcex94XBL, xcex94YBL) below. Based on the above described amount of deviation (xcex94XBL, xcex94YBL), based on the position coordinates (x2, y2) of the mask marks MAM, the center of the visual field of the microscope 14 for mask marks being regarded as the zero point, and based on the position coordinates (x3, y3) of the workpiece marks WAM, the center of the visual field of the microscope 15 for workpiece marks being regarded as the zero point, positioning of the mask marks MAM relative to the workpiece marks WAM can be carried out. Since the middles of the visual fields of the microscope for mask marks 14 and of the microscope for workpiece marks can deviate by the amount (xcex94XBL, xcex94YBL) from one another, as was described above, the mask marks MAM in the state shown in FIG. 8(b) with respect to the workpiece marks WAM deviate by (xcex94XBL+x2xe2x88x92x3, xcex94YBL+y2xe2x88x92y3). As was described above, the mask M and the workpiece W can be positioned relative to one another when, proceeding from the state shown in FIG. 8(b), the workpiece carrier 13 is moved by an amount which corresponds to the amount of deviation (xcex94XBL+x2xe2x88x92x3, xcex94YBL+y2xe2x88x92y3). This process is carried out for each of the two workpiece marks. Two microscopes 15 for the workpiece marks can also be used. However, since the workpiece carrier 13 has the device 13a for X-Y movement, in order to carry out incremental exposure, using it, two workpiece marks can be determined in succession only by a single microscope.
(vii) After completion of positioning of the mask M relative to the workpiece W, the microscope 14 for the mask marks is removed. The mask pattern is exposed onto the workpiece W by emitting exposure light from the light irradiation part 10.
The disadvantages associated with use of an exposure device with the above described arrangement is as follows:
The microscope 14 for the mask marks must be arranged such that it can be inserted or removed between the light irradiation part 10 and the mask M. Therefore, a movement device is needed which carries out insertion or removal. The device and control are therefore complicated.
Furthermore, in general, the reproducibility of the position of the microscope for mask marks during insertion or removal is poor. The microscope for mask marks does not always return to its original position upon insertion after removal. Therefore, it is necessary to carry out the above described baseline correction each time the microscope for mask marks is inserted or removed, thus reducing the throughput.
On the other hand, if the microscope 14 for the mask marks is not inserted or removed, in baseline correction, only the deviation due to thermal expansion or the like need be taken into account. Therefore, baseline correction does not need to be done very often, thus preventing the throughput from decreasing. The microscope 14 for mask marks, however, remains inserted in the optical path from the light irradiation part 10. The area in which this microscope 14 is present becomes a shadow. This means that the effective exposure area is made smaller, and the exposure light cannot be effectively used.
The invention was devised to eliminate the above described disadvantages of the prior art. The primary objects of the present invention are to provide an exposure device in which a device for insertion or removal of the microscope for mask marks is not necessary, in which the arrangement of the device is simplified, and thus, the costs are reduced, in which, furthermore, a reduction of the throughput is prevented, and in which the effective exposure area is prevented from being reduced in size.
The above objects are achieved in accordance with the invention as follows:
(1) In an exposure device which comprises the following:
a microscope for determining the mask alignment marks which determines the mask alignment marks which are formed on a mask;
a microscope for determining the workpiece alignment marks which determines the workpiece alignment marks which are formed on a workpiece; and
a controller which, as a result of the position information of the mask alignment marks which has been determined by the microscope for determining the mask alignment marks, and as a result of the position information of the workpiece alignment marks which has been determined by the microscope for determining the workpiece alignment marks, positions the mask relative to the workpiece,
the above described microscope for determining the mask alignment marks is located in a workpiece carrier and is made such that it moves in one piece with the workpiece carrier, and furthermore a reference mark is located at the position which is the light incidence part of the above described microscope for determining the mask alignment marks and which can be determined by this microscope for determining the mask alignment marks and the microscope for determining the workpiece alignment marks.
(2) The exposure device described above in (1) is an incremental exposure device in which a workpiece which has been divided into several exposure zones is moved incrementally and exposed.
(3) In (1) and (2), the workpiece carrier is provided with a single microscope for determining the mask alignment marks.
(4) In (1), (2), and (3), the above described reference mark consists of frame-like light reflection components which are located in the vicinity of the visual field of the microscope for determining the mask alignment marks and which intersect orthogonally.
(5) In (4), the light reflection components are formed in the vicinity of the visual field of the above described microscope for determining the mask alignment marks by vapor deposition of a transparent part.
As was described above, in accordance with the invention, a microscope for determining mask marks is located in the workpiece carrier and there is a reference mark in its light incidence part. Therefore, a device for insertion or removal of the microscope for determining the mask marks is not necessary. Thus, the arrangement of the device can be simplified.
In the conventional device, there was the disadvantage that when the microscope for determining the mask marks is inserted or removed contaminants and the like fall on the mask and the workpiece. However, in accordance with the invention, this disadvantage does not arise because there need not be a device for insertion or removal.
Furthermore, since the microscope for determining the mask marks is moved together with the workpiece carrier, it is possible to move the microscope for mask marks using the device for moving the workpiece carrier and to determine two mask marks. Therefore, there need not be two microscopes for determining the mask marks, as was the case in the conventional example.
The invention is further described below using several embodiments shown in the drawings.